Gravity measuring instrument



K.- HARTLEY GRAVITY MEASURING INSTRUMENT Original Filed Oct. '3, 1951 3 Sheets-Sheet 1 mvv i llomey K. HARTLEY GRAVITY MASURING INSTRUMENT Original Filed Oct. 3, 1931 3 Sheets-Sheet 2 l /l/F/ lla/ @lu Q ,4 Homey oct. zo, 1936.

originl Filed oct. :5, 19:51

K. HARTLEY GRAVITY MEASURING INSTRUMENT.

5 Sheets-Sheet .'5

Inventor .f1 llorney Reissued Oct. 20, 1936 PATENT OFFICE GRAVITY MEASURING INSTRUMEN Kenneth Hartley, Houston, Tex., assignor, by mesne assignments, to Humble Oil Refining Company, Harris County, Tex., a corporation of Texas Original No. 1,898,534, dated February 21, 1933, Serial No. 566,773, October 3, 1931. Application for reissue February 17, 1934, Serial No. 711,787

5 Claims.

This invention appertains to new and useful improvements in measuring instruments and more particularly to an instrument for measuring `small diil'erences in the force of gravit-y.

The principal object of this invention is to provide a measuring instrument Vfor measuring small diil'erences in the force of gravity with a precision of about one-ten thousandth of a dyne per gram, which is about one-ten millionth of the total force.

Previous attempts to do this have not succeeded in getting better than one part in one hundred thousand; chiey because of difficulties due to temperature eiects and to elastic hysteresis.

During the course of the following specification, other important objects and advantages of the invention will readily become apparent to the reader.

In the drawings:-

Figure 1 represents a side elevational view of the instrument diagrammatically arranged.

Fig. 2 represents a vertical sectional view through the scope. l

Fig. 3 represents a vertical sectional view through the beam looking toward the weight.

Fig. 4 represents a top plan view of the base and beam.

Fig. 5 represents a side elevational view of the base and beam. g

Fig. 6 represents an end elevational view of the base looking toward the mirrors and beam adjusting means having parts omitted.

Referring to the drawings wherein like numerals designate like parts, it can be seen that a Weight 5 is suspended from a spring 6 and ilexibly connected to a very light weighing beam hinged at one end, as at 'I by a pair of phosphorv bronze ribbons while its opposite end carries a pair of small mirrors 8. Light from a small electric lamp 9 at the top of the apparatus passes through a lens IIl and is reflected frorr the mirrors back through the lens to the reflecting prism II and then to the eye piece I2 where an image of the lament of the lamp can be observed.

If the two mirrors 8 are in the same plane, the two images form a single line of light, as seen through the eyepiece, but if they are not in the same plane, the images will not coincide. The mirrorsv are so mounted that -movement of the beam causes them to rotate in opposite directions; thus moving the reiiected images of the lamp in opposite directions each mirror acting as an optical lever while the points of the support one millimeter apart and the distance from (Cl. 26S-1.4)

the mirror to the eyepiece about 600 millimeters so that the magnification is 1200 for each mirror and the apparent relative movement of the two images of the lamp filament is 2400 times the actual movement of the beam.

The tension in the main spring 6 is adjusted by the screw 6. so that it does not quite lift the weight to the zero position but leaves a small fraction of the load (about 1/1000) to be carriedby a light auxiliary spring I3, which may be referred to as the weighing spring.

The tension in this spring I3 is controlled by the micrometer screw I4 atthe top so that small changes in the gravitational pull can be compensated for by altering the tension in the weighing spring so as to bring the mirrors back into the same plane. .This spring I3 is calibrated so that the reading of the micrometer dial I5 gives the actual change in gravitational force in thousandths of a dyne per gram.

A suitable locking mechanism not shown in the drawings, holds the weight accurately in the zero position between observations so that the spring is kept under constant tension'and never relaxes, thus avoiding errors vdue to hysteresis. This mechanism is complex, as each side of the spring must be securely held so that jolting will notprof duce an increased stress in any part. However, such securing means can `be taken care of in numerous ways, and need not form part of the present invention.

The effect of temperature on the spring is compensated for, as far as possible, oy an arrangement-of eiipansionmembers in the frame, similar to the old grid ron compensated pendulum, and then the whole instrument is enclosed in a thermostat which will maintain the temperature constant to within 1/ 1000 of a degree during a whole series of observations. The ordinary laboratory thermostat would not be convenient for field use but a special type can be devised to accompany the device in the field.

The observation scope generally referred to by numeral I6 and which includes the aforementioned lamp 9, prism I I, and eye piece I2, has the eye piece I2 mounted within the horizontal tube I1 which communicates with the vertical tube I8 at the upper end thereof, at which point the prism II and lamp 9 are located.

It can also be observed, that the lamp is provided with a straight lament, so that the image of the lament to the observer will be a straight line of light.

The tube I8 adjusting screw 6s and micrometer screw I4, are carried by the frame I9 and as is apparent in Fig. 1, it is necessary that some form of bearing block 20 be provided between the micrometer I4, and the weighing spring il.

The aforementioned weighing beam. which is denoted by numeral 2i is connected to the frame il or some other suitable support by the ribbon 22 of phosphor bronze or other suitable material. As can be clearly seen in Figs. 4 and 5. the beam is constructed in a light but rigid fashion and is formed ci aluminum or some other suitable light material, so that its weight will be as light as possible.

Numeral 23 represents phosphor bronze ribbons i'or connecting the mirrors l to the beam 2i and stationary supports 24.

' invention in specific terms, it is to be understood that numerous changes in the shape. size andmaterials may be resorted to without departing from the spirit and scope of the invention as claimed hereinafter.

Having thus described my invention, what I claim as new isz- 1. An instrument for measuring small variations in gravitational attraction comprising grav'- ity responsive means, means indicative of the position of the rst means, elastic means exerting on the rst means a` major eiIort opposing the force exerted by gravity on the ilrst means tlie ilrst means a maior effort opposing and approximately balancing the force exerted by gravity on the iirst means to insure equilibrium o! the irst means within a narrow range of positions for variations of gravitational attraction of substantial magnitudes. means exerting on the rst means an adjustable minor eil'ort'to attain equilibrium with the iii-st means at a determinable position, and means whereby the efiort exerted by the last named means may be determined. n

3. An instrument for measuring small variations in gravitational attraction comprising gravity responsive means, means indicative of the position of the ilrst means, a spring exerting on the ilrst means a major eil'ort opposing and approximately balancing the force exerted by grav- `ity on the ilrst means to insure equilibrium oi' the first means within a narrow range of positions for variations of gravitational attraction of substantial magnitudes, a second spring exerting on the first means an adjustable minor eiort to attain equilibrium.with the first means at a determinable position, and means whereby the effort exerted by the second spring may be detex-mined.

4. An instrument for measuring small variations in gravitational attraction including a gravity responsive system comprising a pivoted beam and a mass connected to the beam, means indicative of the mechanical condition of the system, a spring exerting on the system a major effort opposing and approximately balancing the force exerted byv gravity thereon to insure equilibrium of the mass withina `narrow range of positions for variations of gravitational attraction of substantial magnitudes, means exerting on the system a minor eifort to attain equilibrium with the system in a determinable mechanical condition, and means whereby the effort exerted by the last named means may be determined.

5. An instrument for 4measuringsmall variations ingravitational attraction including a gravity responsive system comprising a pivoted beam and a mass connected to the beam, means indicative oi' the mechanical' condition of the system, a spring exerting on the system a major eiIort opposing and approximately balancing the force exerted by gravity thereon to insure equilibrium of the mass within a narrow range of positions for variations of gravitational attraction oi'substantial magnitudes, a second spring exerting on the system a vminor eort to attain equilibrium with the system in a determinable mechanical condition, and means whereby the efiort exerted by the second spring may be de" termined. l

KENNETH HARTLEY. 

